1. Field of the Invention
The present invention relates to a liquid ejecting head for ejecting liquid so as to perform printing on a print medium, a substrate for a liquid ejecting head, and a printing apparatus.
2. Description of the Related Art
A printing apparatus of an ink jet type having a system for ejecting liquid by use of generation of bubbles produced by thermal energy generated by a heat generating resistor element in liquid is currently adopted in many cases.
In the printing apparatus of this type, a heat generator in the heat generating resistor element during liquid ejection is exposed to high temperature, and further, undergoes a cavitation impact according to bubble formation and shrinkage in liquid or a chemical reaction of ink in combination. Therefore, the heat generating resistor element is provided with an upper protective layer in such a manner as to cover the heat generating resistor element, so as to protect a heat generating resistor portion from the cavitation impact during defoaming or the chemical reaction of ink. Since the temperature rises up to about 700° C. at the surface of the upper protective layer, a colorant, an additive, and the like contained in the ink are heated at high temperature, and then, are decomposed on a molecular level into a slightly soluble substance called “kogation” which may adhere to the surface of the upper protective layer. When the kogation adheres onto the upper protective layer, thermal conduction from the heat generating resistor element to the ink becomes uneven in each region, and therefore, bubble formation may be unstabilized. Moreover, since the thermal conduction from the heat generating resistor element to the ink becomes insufficient by adherence of kogation, the velocity of the ejected ink does not become satisfactory, thereby possibly degrading an ink landing accuracy.
In view of the above-described circumstance, Japanese Patent Laid-Open No. 2008-105364 discloses a print head having an upper protective layer made of iridium or ruthenium. In this print head, in a case where kogation or the like adheres to the surface of the upper protective layer, the surface is dissolved by an electrochemical reaction, thus removing the kogation adhering to the surface of the upper protective layer.